My present invention pertains generally to venting devices. More particularly, the invention relates to a very effective and practical vent structure for use in the control pins of a liquid metal fast breeder reactor (LMFBR), for example, and to a novel method of fabricating the vent structure.
As is well known, helium (He) is generated in the LMFBR control pins as the result of a neutron, alpha (n,.alpha.) reaction on boron (B). This helium is generated in each pin up to the rate of 3 cc/hr or 72 cc/day volume at standard temperature and pressure (STP). If all of this generated gas is released from the boron carbide (B.sub.6 C) matrix of a control pin, the resulting 26 liters per year poses a serious containment and pressure problem using closed control pins, especially since sudden onsets of extreme pressure could develop during the reactor power cycles. Conversely, the use of open control pins allows the boron carbide to come into direct contact with the high temperature sodium (Na) liquid metal coolant with the resulting attack thereon and likelihood of boron contamination of the coolant.
A suitable vent structure for use with a reactor control pin and a vent structure fabrication method are shown, described and claimed by the inventor in his copending U.S. patent application Ser. No. 296,680 filed on Oct. 11, 1972 for Vent Assembly and now U.S. Pat. No. 3,876,403. While such disclosed vent structure and fabrication method are entirely satisfactory, a vent structure providing more precise flow characteristics therethrough, and which structure can be more consistently and easily fabricated to produce an accurate predetermined flow, is desirable and useful in certain applications.